The present invention relates generally to a process for determining and evaluating the combustion pressure, and, more particularly, to a process for measuring the incremental pressure caused by combustion in such a way that the ignition angle can be accurately adjusted even if the pressure sensors are not particularly accurate. [as generically defined by the preamble to claim 1.]
Processes for determining the combustion chamber are known in which very sturdy, accurate sensors are used. Particularly if the combustion pressure is to be used for controlling and/or monitoring engine functions, the requirements for accuracy of the measured pressure values are very stringent. It is also essential that the measurement sensitivity and accuracy be constant over a wide temperature range. The known processes therefore have the disadvantage that very expensive sensors must be used, if the measure pressure values are to be usable for controlling and/or monitoring the engine.
From Patent Abstracts of Japan, Vol. 9, No. 320 (p-413) (2043), Dec. 14, 1985, JP-A 60 147 631, an apparatus for determining the combustion pressure is known. To this end, on the one hand the pressure in the combustion chamber is detected by means of a pressure sensor; on the other, the compression pressure at specific crankshaft angle positions is calculated continuously. By subtracting the compression pressure from the measured combustion chamber pressure, the combustion pressure can then be determined, which is finally used for determining the instant of ignition. This apparatus thus requires computer-aided determination of the compression pressure and makes use of variables that are not stable for long periods of time, because over the life of an internal combustion engine, sealing problems repeatedly occur at inlet and outlet valves, and moreover the piston rings are subject to wear over the life of the engine.